The following abbreviations are herewith defined, at least some of which are referred to within the following description of the state-of-the-art and the present invention.    ECT Equal Cost Tree    EHEC Equal-Hop, Equal-Cost    IEEE Institute of Electrical and Electronics Engineers    I-SID service instance identifier    LAN Local Area Network    SPB Shortest Path Bridging    VID VLAN ID    VLAN Virtual Local Area Network    WAN Wide Area Network
Communication networks such as LANs (local area networks) and WANs (wide area networks) frequently include a large number of interconnected devices. These devices may communicate with each other thorough the network so that, for example, client workstations such as PCs (personal computers) can communicate with each other or with servers in order to access information stored there or take advantage of their larger computing resources. Examples of such networks include those deployed by business enterprises or public or private institutions such as hospitals and universities.
In this type of communications environment, each network device is typically not connected directly to each other device, unless the network is very small. In most installations, such devices generally communicate with each other through a number, and sometimes a large number of nodes such as bridges, hubs, and switches. Because of the manner in which these devices are interconnected, communications through the network may be able to take any one of two or more paths. An efficient manner of directing communications to the appropriate recipient therefore becomes important.
STP (spanning tree protocol) and its numerous variants were developed to map out efficient paths through the network, and also to prevent loops where data traffic traversing the network may be forwarded to the same node more than once during the attempt to transmit it from a source to a destination. While it is advantageous to prevent loops and find the lowest cost paths available, STP will often block the use of some links between network devices as redundant. When the failure of a link or network occurs, the paths are recalculated and the redundant links may be utilized, but otherwise they represent an inefficient use of network resources.
More recently, SPB (shortest path bridging) as described primarily in the protocol IEEE 802.1aq uses a path mapping scheme that utilizes redundant paths by determining a number of EHEC (equal-cost, equal-hop) paths thought the network from a given source bridge to a particular destination bridge, and assigning each VLAN (virtual local area network) to one of one or more EHEC paths. A VLAN creates a broadcast domain for Ethernet traffic through the network by identifying certain intermediate bridges for use by the VLAN traffic. A VLAN may be associated with, for example, a particular department or customer. Loops are avoided because the data traffic always takes the specified path. At the same time, other VLANs may be assigned to otherwise redundant paths through the network.
IEEE 802.1aq specifies a number of ECT (equal cost tree) protocols in order to assign paths to individual VLANS. While these protocols do perform this function, they do in some situations fail to fully utilize all available paths when making these assignments. A manner of making path assignments that at least avoids these limitations and makes more robust use of network resources is therefore needed.
Note that the techniques or schemes described herein as existing or possible are presented as background for the present invention, but no admission is made thereby that these techniques and schemes were heretofore commercialized or known to others besides the inventors.
Accordingly, there has been and still is a need to address the aforementioned shortcomings and other shortcomings associated with selecting network communication paths for VLANs or other groups of data traffic. These needs and other needs are satisfied by the present invention.